Colorectal Cancer: Radiation Therapy

Pictured: Karyn Goodman Karyn Goodman is part of Memorial Sloan Kettering's radiation oncology team using sophisticated tools to deliver radiation directly to rectal tumors while minimizing injury to normal tissue.

Radiation therapy — the use of high-energy beams or seeds to eliminate tumors – is an important part of treatment for rectal cancer. Memorial Sloan Kettering’s radiation oncology team uses sophisticated, highly precise tools to deliver powerful doses of radiation directly to tumors while avoiding damage to healthy tissues.

Radiation therapy can be used in various ways for the treatment of rectal cancer:

  • Most rectal cancer patients receive radiation before surgery to shrink tumors and make them easier to remove.
  • Radiation therapy is occasionally used in place of surgery to destroy rectal tumors in patients who are not good candidates for surgery.
  • In advanced metastatic rectal cancer, radiation therapy may also be used to relieve symptoms such as intestinal blockage, bleeding, or pain.

Whether you have an early-stage tumor or more-advanced rectal cancer, Memorial Sloan Kettering offers several radiation therapy options. These include:

Our doctors will work with you and other members of your treatment team to help you decide which approach, or combination of approaches, is best for you.

Radiation oncologists work closely with medical physicists to plan each radiation treatment. This ensures that the correct dose of radiation is delivered precisely where it is needed. Advances in technology have made it possible to eliminate rectal tumors while also limiting the risk of damage to other tissue that could lead to urinary, bowel, and sexual side effects.

Because our radiation oncologists are continually working to advance the field, we also offer some patients access to clinical trials of new approaches to radiation therapy. By participating in a clinical trial, you may have access to radiation therapy techniques or combinations of therapies that are not yet widely available.

External-Beam Radiation Therapy

In external-beam radiation, a highly focused beam of radiation is delivered to the tumor from a source outside the body. External-beam radiation is the most common type of radiation therapy used for rectal cancer treatment. It is also an important part of treatment for patients with recurrent rectal cancer who received radiation as part of their initial treatment.

Newer radiation techniques can reduce radiation exposure to the pelvic bones, decreasing the risk of osteoporosis.

Intensity-Modulated Radiation Therapy (IMRT)

IMRT is a type of 3-D radiation therapy that targets tumors with greater precision than conventional external-beam radiation therapy. IMRT uses highly sophisticated computer software and 3-D images from CT scans to deliver multiple beams of highly focused radiation from different angles, rather than a single, large, uniform beam.

At Memorial Sloan Kettering, we use IMRT in patients with anal cancer, low-lying rectal cancers, or rectal cancer that has recurred after surgery. Patients with anal and rectal cancers may also receive chemotherapy drugs that sensitize the tumor to the effects of radiation.

Image-Guided Radiation Therapy (IGRT)

Patients with recurrent rectal cancer who have had prior radiation therapy to the pelvis may receive radiation treatment with an advanced imaging technique called IGRT. With IGRT, small markers are implanted in the body and their location is verified using a CT scanner immediately before each treatment. These markers guide the delivery of the radiation. Because radiation with IGRT is highly focused, radiation therapy can be completed in as few as three treatments.

Internal Radiation Therapy

In internal radiation therapy, radiation is placed close to the tumor from a location inside the body. There are two types of internal radiation therapy for rectal cancer: intraoperative radiation therapy and endorectal brachytherapy.

Intraoperative Radiation Therapy (IORT)

Intraoperative radiation therapy takes place during surgery to remove a rectal tumor. While the patient is still in the operating room, a machine called a linear accelerator delivers a concentrated beam or electron radiation to the area where cancer cells could still be lurking. Because this treatment is conducted during the surgical procedure and can be delivered to a precisely defined area, it is possible to use a higher-than-usual — and therefore more effective — dose of radiation and to spare nearby healthy tissues. (Patients receiving IORT usually also receive external-beam radiation therapy prior to the operation.)

IORT is used to treat selected patients whose rectal cancer has recurred in the pelvis after an initial treatment with surgery and radiation therapy.

Endorectal Brachytherapy

Endorectal brachytherapy is now an option for some Memorial Sloan Kettering patients who have recurrent rectal cancer but are not good candidates for surgery. A radioactive source is temporarily introduced into the rectum through an applicator to deliver a high dose of radiation to a confined site. The radioactivity is highly localized, minimizing radiation exposure in the surrounding healthy tissue. (This approach resembles radioactive seed implantation for prostate cancer.)